Bought this machine a few days ago and used it 3 days in a row grinding a bunch of hard concrete basements with a 30# grit diamond discs soft bond, very aggressive to the concrete putting the machine on the limit. I have seen some people mention that the machine gets weak and kinda stops and found that happens because the diamond discs that comes with the machine are very aggressive and sometimes can also be your extension cord, use a 12gauge one. Otherwise the machine is awesome and if you wanna run it very smooth use a higher grit# diamonds like 60# 80# with 3 arrows shapes.